Anthony J. Blazevich

The ABC of Physical Activity for Health: A consensus statement from the British Association of Sport and Exercise Sciences

Absract Our understanding of the relationship between physical activity and health is constantly evolving. Therefore, the British Association of Sport and Exercise Sciences convened a panel of experts to review the literature and produce guidelines that health professionals might use. In the ABC of Physical Activity for Health, A is for All healthy adults, B is for Beginners, and C is for Conditioned individuals. All healthy adults aged 18–65 years should aim to take part in at least 150 min of moderate-intensity aerobic activity each week, or at least 75 min of vigorous-intensity aerobic activity per week, or equivalent combinations of moderate- and vigorous-intensity activities. Moderate-intensity activities are those in which heart rate and breathing are raised, but it is possible to speak comfortably. Vigorous-intensity activities are those in which heart rate is higher, breathing is heavier, and conversation is harder. Aerobic activities should be undertaken in bouts of at least 10 min and, ideally, should be performed on five or more days a week. All healthy adults should also perform muscle-strengthening activities on two or more days a week. Weight training, circuit classes, yoga, and other muscle-strengthening activities offer additional health benefits and may help older adults to maintain physical independence. Beginners should work steadily towards meeting the physical activity levels recommended for all healthy adults. Even small increases in activity will bring some health benefits in the early stages and it is important to set achievable goals that provide success, build confidence, and increase motivation. For example, a beginner might be asked to walk an extra 10 min every other day for several weeks to slowly reach the recommended levels of activity for all healthy adults. It is also critical that beginners find activities they enjoy and gain support in becoming more active from family and friends. Conditioned individuals who have met the physical activity levels recommended for all healthy adults for at least 6 months may obtain additional health benefits by engaging in 300 min or more of moderate-intensity aerobic activity per week, or 150 min or more of vigorous-intensity aerobic activity each week, or equivalent combinations of moderate- and vigorous-intensity aerobic activities. Adults who find it difficult to maintain a normal weight and adults with increased risk of cardiovascular disease or type 2 diabetes may in particular benefit from going beyond the levels of activity recommended for all healthy adults and gradually progressing towards meeting the recommendations for conditioned individuals. Physical activity is beneficial to health with or without weight loss, but adults who find it difficult to maintain a normal weight should probably be encouraged to reduce energy intake and minimize time spent in sedentary behaviours to prevent further weight gain. Children and young people aged 5–16 years should accumulate at least 60 min of moderate-to-vigorous-intensity aerobic activity per day, including vigorous-intensity aerobic activities that improve bone density and muscle strength.

Intra- and intermuscular variation in human quadriceps femoris architecture assessed in vivo

Despite the functional importance of the human quadriceps femoris in movements such as running, jumping, lifting and climbing, and the known effects of muscle architecture on muscle function, no research has fully described the complex architecture of this muscle group. We used ultrasound imaging techniques to measure muscle thickness, fascicle angle and fascicle length at multiple regions of the four quadriceps muscles in vivo in 31 recreationally active, but non‐strength‐trained adult men and women. Our analyses revealed a reasonable similarity in the superficial quadriceps muscles, which is suggestive of functional similarity (at least during the uni‐joint knee extension task) given that they act via a common tendon. The deep vastus intermedius (VI) is architecturally dissimilar and therefore probably serves a different function(s). Architecture varies significantly along the length of the superficial muscles, which has implications for the accuracy of models that assume a constant intramuscular architecture. It might also have consequences for the efficiency of intra‐ and intermuscular force transmission. Our results provide some evidence that subjects with a given architecture of one superficial muscle, relative to the rest of the subject sample, also have a similar architecture in other superficial muscles. However, this is not necessarily true for vastus lateralis (VL), and was not the case for VI. Therefore, the relative architecture of one muscle cannot confidently be used to estimate the relative architecture of another. To confirm this, we calculated a value of whole quadriceps architecture by four different methods. Regardless of the method used, we found that the absolute or relative architecture of one muscle could not be used as an indicator of whole quadriceps architecture, although vastus medialis, possibly in concert with VL and the anterior portion of VI, could be used to provide a useful snapshot. Importantly, our estimates of whole quadriceps architecture show a gender difference in whole quadriceps muscle thickness, and that muscle thickness is positively correlated with fascicle angle whereas fascicle length is negatively, although weakly, correlated with fascicle angle. These results are supportive of the validity of estimates of whole quadriceps architecture. These data are interpreted with respect to their implications for neural control strategies, region‐specific adaptations in muscle size in response to training, and gender‐dependent differences in the response to exercise training.

Effect of Acute Static Stretch on Maximal Muscle Performance: A Systematic Review

INTRODUCTION The benefits of preexercise muscle stretching have been recently questioned after reports of significant poststretch reductions in force and power production. However, methodological issues and equivocal findings have prevented a clear consensus being reached. As no detailed systematic review exists, the literature describing responses to acute static muscle stretch was comprehensively examined. METHODS MEDLINE, ScienceDirect, SPORTDiscus, and Zetoc were searched with recursive reference checking. Selection criteria included randomized or quasi-randomized controlled trials and intervention-based trials published in peer-reviewed scientific journals examining the effect of an acute static stretch intervention on maximal muscular performance. RESULTS Searches revealed 4559 possible articles; 106 met the inclusion criteria. Study design was often poor because 30% of studies failed to provide appropriate reliability statistics. Clear evidence exists indicating that short-duration acute static stretch (<30 s) has no detrimental effect (pooled estimate = -1.1%), with overwhelming evidence that stretch durations of 30-45 s also imparted no significant effect (pooled estimate = -1.9%). A sigmoidal dose-response effect was evident between stretch duration and both the likelihood and magnitude of significant decrements, with a significant reduction likely to occur with stretches ≥ 60 s. This strong evidence for a dose-response effect was independent of performance task, contraction mode, or muscle group. Studies have only examined changes in eccentric strength when the stretch durations were >60 s, with limited evidence for an effect on eccentric strength. CONCLUSIONS The detrimental effects of static stretch are mainly limited to longer durations (≥ 60 s), which may not be typically used during preexercise routines in clinical, healthy, or athletic populations. Shorter durations of stretch (<60 s) can be performed in a preexercise routine without compromising maximal muscle performance.

Effects of Physical Training and Detraining, Immobilisation, Growth and Aging on Human Fascicle Geometry

AbstractIn addition to its size and the extent of its neural activation, a muscle’s geometry (the angles and lengths of its fibres or fascicles) strongly influences its force production characteristics. As with many other tissues within the body, muscle displays significant plasticity in its geometry. This review summarises geometric differences between various athlete populations and describes research examining the plasticity of muscle geometry with physical training, immobilisation/ detraining, growth and aging. Typically, heavy resistance training in young adults has been shown to cause significant increases in fascicle angle of vastus lateralis and triceps brachii as measured by ultrasonography, while high-speed/ plyometrics training in the absence of weight training has been associated with increases in fascicle length and a reduction in angles of vastus lateralis fascicles. These changes indicate that differences in geometry between various athletic populations might be at least partly attributable to their differing training regimes. Despite some inter-muscular differences, detraining/unloading is associated with decreases in fascicle angle, although little change was shown in muscles such as vastus lateralis and triceps brachii in studies examining the effects of prolonged bed rest. No research has examined the effects of other interventions such as endurance or chronic stretching training. Few data exist describing geometric adaptation during growth and maturation, although increases in gastrocnemius fascicle angle and length seem to occur until maturation in late adolescence. Although some evidence suggests that a decrease in both fascicle angle and length accompanies the normal aging process, there is a paucity of data examining the issue; heavy weight training might attenuate the decline, at least in fascicle length. A significant research effort is required to more fully understand geometric adaptation in response to physical training, immobilisation/detraining, growth and aging.

Moderate-duration static stretch reduces active and passive plantar flexor moment but not Achilles tendon stiffness or active muscle length

The effects of static stretch on muscle and tendon mechanical properties and muscle activation were studied in fifteen healthy human volunteers. Peak active and passive moment data were recorded during plantar flexion trials on an isokinetic dynamometer. Electromyography (EMG) monitoring of the triceps surae muscles, real-time motion analysis of the lower leg, and ultrasound imaging of the Achilles-medial gastrocnemius muscle-tendon junction were simultaneously conducted. Subjects performed three 60-s static stretches before being retested 2 min and 30 min poststretch. There were three main findings in the present study. First, peak concentric moment was significantly reduced after stretch; 60% of the deficit recovered 30 min poststretch. This was accompanied by, and correlated with (r = 0.81; P < 0.01) reductions in peak triceps surae EMG amplitude, which was fully recovered at 30 min poststretch. Second, Achilles tendon length was significantly shorter during the concentric contraction after stretch and at 30 min poststretch; however, no change in tendon stiffness was detected. Third, passive joint moment was significantly reduced after stretch, and this was accompanied by significant reductions in medial gastrocnemius passive muscle stiffness; both measures fully recovered by 30 min poststretch. These data indicate that the stretching protocol used in this study induced losses in concentric moment that were accompanied by, and related to, reductions in neuromuscular activity, but they were not associated with alterations in tendon stiffness or shorter muscle operating length. Reductions in passive moment were associated with reductions in muscle stiffness, whereas tendon mechanics were unaffected by the stretch. Importantly, the impact on mechanical properties and neuromuscular activity was minimal at 30 min poststretch.

Lack of human muscle architectural adaptation after short-term strength training

The mechanisms governing the increases in force production in response to short periods of strength training have yet to be fully elucidated. We examined whether muscle architectural adaptation was a contributing factor. Ultrasound imaging techniques were used to measure quadriceps muscle architecture at 17 sites in vivo in trained and untrained legs of men and women after 2.5 and 5 weeks of unilateral knee extension training, as well as in a nontraining control group. Despite increases in knee extensor strength of the trained and untrained (women only) legs, there were no changes in muscle thickness, fascicle angle, or fascicle length in any of the muscles tested. The moderate correlation between vastus lateralis thickness (middle site) and eccentric (r = 0.55; P < 0.05) and concentric (r = 0.46; P < 0.1) torque after, but not before, training is suggestive of neural rather than architectural adaptations predominating in the early phase of training. Muscle Nerve, 2006

The effect of contrast water therapy on symptoms of delayed onset muscle soreness

This study examined the effect of contrast water therapy (CWT) on the physiological and functional symptoms of delayed onset muscle soreness (DOMS) following DOMS-inducing leg press exercise. Thirteen recreational athletes performed 2 experimental trials separated by 6 weeks in a randomized crossover design. On each occasion, subjects performed a DOMS-inducing leg press protocol consisting of 5 X 10 eccentric contractions (180 seconds recovery between sets) at 140% of 1 repetition maximum (1RM). This was followed by a 15-minute recovery period incorporating either CWT or no intervention, passive recovery (PAS). Creatine kinase concentration (CK), perceived pain, thigh volume, isometric squat strength, and weighted jump squat performance were measured prior to the eccentric exercise, immediately post recovery, and 24, 48, and 72 hours post recovery. Isometric force production was not reduced below baseline measures throughout the 72-hour data collection period following CWT (∼4–10%). However, following PAS, isometric force production (mean ± SD) was 14.8 ± 11.4% below baseline immediately post recovery (p > 0.05), 20.8 ± 15.6% 24 hours post recovery (p > 0.05), and 22.5 ± 12.3% 48 hours post recovery (p > 0.05). Peak power produced during the jump squat was significantly reduced (p > 0.05) following both PAS (20.9 ± 13.4%) and CWT (12.8 ± 8.0%), with the mean reduction in power for PAS being marginally (not significantly) greater than for CWT (effect size = 0.76). Thigh volume measured immediately following CWT was significantly less than PAS. No significant differences in the changes in CK were found; in addition, there were no significant (p > 0.01) differences in perceived pain between treatments. Contrast water therapy was associated with a smaller reduction, and faster restoration, of strength and power measured by isometric force and jump squat production following DOMS-inducing leg press exercise when compared to PAS. Therefore, CWT seems to be effective in reducing and improving the recovery of functional deficiencies that result from DOMS, as opposed to passive recovery.

The relationship between changes in interstitial creatine kinase and game-related impacts in rugby union

Aim: The primary purpose of this study was to investigate the relationship between the pre-game to post-game changes in creatine kinase concentration (Δ[CK]) and impact-related game statistics in elite rugby union players. Methods: Twenty-three elite male rugby union players each provided interstitial fluid samples obtained via electrosonophoresis (ESoP) 210 min before and within a maximum time of 30 min after up to five rugby union games. Specific game statistics that were deemed to be important in determining the relationship between impact and [CK] were obtained from AnalyRugby software for each individual player. Regression equations to predict Δ[CK] from game statistics were created using a backwards random-effects maximum likelihood regression. Results: The Δ[CK] (mean (SD)) from pre-game to post-game was 926.8 (204.2) IU. Game time and time defending were significantly correlated to Δ[CK] in both the forwards and backs. The predicted Δ[CK] (mean (95% confidence limit)) was 1439.8 (204.9) IU for the forwards and 545.3 (78.0) IU for the backs and was significantly correlated with the actual Δ[CK] (r = 0.69 and r = 0.74). Conclusions: CK increased from pre-game to post-game in a position-specific manner. A large proportion of the Δ[CK] can be explained by physical impact and thus can be predicted using a prescribed number of game statistics. As the Δ[CK] is an indicator of muscle damage, the prediction of Δ[CK] provides a theoretical basis for recovery strategies and adjustment of subsequent training sessions after rugby union games.

EFFECT OF CONTRACTION MODE OF SLOW-SPEED RESISTANCE TRAINING ON THE MAXIMUM RATE OF FORCE DEVELOPMENT IN THE HUMAN QUADRICEPS

This study examined the effects of slow‐speed resistance training involving concentric (CON, n = 10) versus eccentric (ECC, n = 11) single‐joint muscle contractions on contractile rate of force development (RFD) and neuromuscular activity (EMG), and its maintenance through detraining. Isokinetic knee extension training was performed 3 · week−1 for 10 weeks. Maximal isometric strength (+11.2%) and RFD (measured from 0–30/50/100/200 ms, respectively; +10.5%–20.5%) increased after 10 weeks (P < 0.01–0.05); however, there was no effect of training mode. Peak EMG amplitude and rate of EMG rise were not significantly altered with training or detraining. Subjects with below‐median normalized RFD (RFD/MVC) at 0 weeks significantly increased RFD after 5‐ and 10‐weeks training, which was associated with increased neuromuscular activity. Subjects who maintained their higher RFD after detraining also exhibited higher activity at detraining. Thus, only subjects with a lesser ability to rapidly attain their maximum force before training improved RFD with slow‐speed resistance exercise. Muscle Nerve, 2008

Age-related changes in mechanical properties of the Achilles tendon.

The stiffness of a tendon, which influences muscular force transfer to the skeleton and increases during childhood, is dependent on its material properties and dimensions, both of which are influenced by chronic loading. The aims of this study were to: (i) determine the independent contributions of body mass, force production capabilities and tendon dimensions to tendon stiffness during childhood; and (ii) descriptively document age‐related changes in tendon mechanical properties and dimensions. Achilles tendon mechanical and material properties were determined in 52 children (5–12 years) and 19 adults. Tendon stiffness and Young’s modulus (YM) were calculated as the slopes of the force–elongation and stress‐strain curves, respectively. Relationships between stiffness vs. age, mass and force, and between YM vs. age, mass and stress were determined by means of polynomial fits and multiple regression analyses. Mass was found to be the best predictor of stiffness, whilst stress was best related to YM (< 75 and 51% explained variance, respectively). Combined, mass and force accounted for up to 78% of stiffness variation. Up to 61% of YM variability could be explained using a combination of mass, stress and age. These results demonstrate that age‐related increases in tendon stiffness are largely attributable to increased tendon loading from weight‐bearing tasks and increased plantarflexor force production, as well as tendon growth. Moreover, our results suggest that chronic increases in tendon loading during childhood result in microstructural changes which increase the tendon’s YM. Regarding the second aim, peak stress increased from childhood to adulthood due to greater increases in strength than tendon cross‐sectional area. Peak strain remained constant as a result of parallel increases in tendon length and peak elongation. The differences in Achilles tendon properties found between adults and children are likely to influence force production, and ultimately movement characteristics, which should be explicitly examined in future research.